This invention relates generally to imaging systems and more particularly to systems and methods for correcting a positron emission tomography (PET) emission image.
The systems and methods are directed toward multi-modal imaging systems capable of scanning using different modalities, such as, for example, but not limited to, Positron Emission Tomography (PET) and Computed Tomography (CT). The difference between multi-mode and multi-modality is that multi-mode systems are utilized to perform scans in different modes, for example, a flouro mode and a tomosynthesis mode, while a multi-modal system is utilized to perform scans in different modalities, for example, CT and PET. It is contemplated that the benefits of systems and methods for analyzing an abnormality of an, object accrue to all multi-modal imaging systems, such as, for example, but not limited to, a PET-CT imaging system.
PET has gained significant popularity in nuclear medicine because of the ability to non-invasively study physiological processes within a body of a patient. PET exhibits a high level of quantification accuracy, among nuclear medicine imaging instruments available. Applications requiring this accuracy include those in the fields of oncology, cardiology and neurology.
Using compounds such as 11C-labeled glucose, 18F-labeled glucose, 13N-labeled ammonia and 15O-labeled water, PET can be used to study such physiological phenomena as blood flow, tissue viability, and in vivo brain neuron activity. Positrons emitted by these neutron deficient compounds interact with free electrons in the body area of interest, resulting in the annihilation of the positron. This annihilation yields the simultaneous emission of a pair of photons approximately 180 degrees apart. A compound having the desired physiological effect is administered to the patient, and the radiation resulting from annihilation is detected by a PET tomography. After acquiring these annihilation “event pairs” for a period of time, the isotope distribution in a cross section of the body can be reconstructed.
PET data acquisition occurs by detection of both photons emitted from the annihilation of the positron in a coincidence scheme. Due to the approximate 180 degree angle of departure from the annihilation site, the location of the two detectors registering the “event” define a chord passing through the location of the annihilation. By histogramming these lines of response, a “sinogram” is produced that may be used by a process of back-projection to produce a three dimensional image of the activity. Detection of these lines of activity is performed by a coincidence detection scheme. A valid event line is registered if both photons of an annihilation are detected within a coincidence window of time. Coincidence detection methods ensure that an event line is histogrammed only if both photons originate from the same positron annihilation.
In CT, an external x-ray source is caused to be passed around the patient. Detectors around the patient then respond to x-ray transmission through the patient to produce an image of an area of study. Unlike PET, which are emission tomography techniques because they rely on detecting radiation emitted from the patient, CT is a transmission tomography technique which utilizes only a radiation source external to the patient.